The present invention relates to novel compounds having activity as orally active metal chelators, particularly iron chelators, to pharmaceutical compositions containing these and to their use in treating disorders associated with iron distribution, particular disorders involving excess of iron and presence of iron dependent parasites.
Members of the hydroxypyridone class are well known for their ability to chelate iron in physiological environment and these have reported as useful in treating iron related disorders such as thalassaemia. For example, see U.S. Pat. Nos. 4,840,958, 5,480,894 and Hider et al (1996) Acta Haematologica 95:6-12. By virtue of their low molecular weight and high affinity for iron (III) these compounds now provide the possibility of removing iron from iron overloaded patients with the hope of providing oral activity. Related compounds for such use are disclosed in U.S. Pat. No. 4,585,780 wherein the characteristics required for oral activity are discussed further.
Two particular compounds referred to by Hider et al, CP20 and CP94 (see Tables 1 and 2 herein), have proved to be effective in man, but both have disadvantages in that they are rapidly inactivated by phase II metabolism and are able to cross the placenta and blood brain barrier. The extensive biotransformation of these compounds is reflected by their limited ability excess body iron in thalassaemic patients.
The requirements for orally active chelators are set out in Table 4 of Hider et al as (i) good absorption from tile gastrointestinal tract, (ii) efficient liver extraction, (iii) poor entry into peripheral cells such as thymus, muscle, heart and bone marrow and (iv) poor ability to penetrate the blood-brain barrier and maternal/placental barriers. This reference refers to desired partition coefficients (Kpart), herein referred to as distribution coefficient values (D pH7.4), for these properties as (i)  greater than 0.2, (ii)  greater than 1.0, (iii)  less than 0.001 and (iv)  less than 0.001, respectively rendering one compound seemingly unsuited to satisfying all four criteria. Hider et suggest the pro-drag strategy to be one possible route forward but no specific compounds have so far been found to meet all criteria.
Pivalic acid esters of hydroxyalkyl substituted 3-hydroxypyridin-4ones have been studied as pro-drugs and found to lead to efficient excretion of iron, in bile and urine, but as reported by Hider et al these are now thought to potentially interfere with the carnitine cycle and thus may not be suitable for use in regular and/or large doses in man.
It is known that the 2-(1xe2x80x2-hydroxyethyl) metabolite of 1,2-diethyl-3-hydroxypyridin-4-one (CP94) produced in rat is an active iron chelator (see Singh et al (1992) Drug Metabolism and Disposition Vol 20. No 2, page 256-261). EP 0494754 A proposes 1-hydroxyethyl as one of many possible substituents at any of the pyridin-4-one positions 1, 2, 5 or 6 for use as iron chelator in treatment of malaria; none of these compounds are however exemplified as made or tested for activity. EP 0768302 A (Novartis) describes a series of related 3-hydroxypyridin-4-ones in which the 2-position is substituted by a methyl group which carries an optionally substituted phenyl or heteroyl ring and a free or esterified hydroxy group. The phenyl or heteroyl group is taught as an essential element of these compounds.
The present inventors now have provided a group of 3-hydroxypyridin-4-one iron chelators having improved properties as compared to the prior art as assessed against the criteria set out above. The preferred compounds of the invention are all characterised by meeting a further criterion (v) in so far as they have a pM for Iron III, i.e. affinity for iron as Fe III, of at least 20, preferably in excess of 23. Preferred compounds have efficiency of iron mobilisation of in excess of 52% when given orally to rats. The definition of pM used herein is the negative log concentration of ferric ion in solution when the total amount of iron equals 10xe2x88x926 M and the concentration of ligand is 10xe2x88x925 M and pH is 7.4.
The present compounds offer the prospect of effective pharmaceutical formulations having reduced levels of active agent, with particular properties of selective targeting of the chelating activity to tissues where the iron level requires alteration, particularly the liver. A particular property of preferred compounds of the invention is that they are not significantly metabolised through conjugation and, in some preferred forms, are provided as prodrugs.
Thus in a first aspect of the present invention there is provided a novel 3-hydroxypyridin-4-one compound or derivative thereof of formula I 
wherein
R is hydrogen or a group that is removed by metabolism in vivo to provide the free hydroxy compound,
R1 is an aliphatic hydrocarbon group or an atiphatic hydrocarbon group substituted by a hydroxy group or a carboxylic acid ester, sulpho acid ester or a C1-6 alkoxy, C6-aryloxy or C7-10aralkoxy ether thereof, and
R3 is selected from hydrogen and C1-6 alkyl;
characterised in that
R2 is selected from groups
(i) xe2x80x94CONHxe2x80x94R5 (ii) xe2x80x94CR6R6OR7 (iii) xe2x80x94CONHCOR5 and (iv) xe2x80x94CON(CnH2n+1)2 
R4 is selected from hydrogen, C1-6 alkyl and a group as described for R2;
R5 is selected from hydrogen and optionally hydroxy, alkoxy, aryloxy or aralkoxy substituted C1-13 alkyl, aryl and C7-13 aralkyl,
R6 is independently selected from hydrogen and C1-13alkyl,
R7 is selected from hydrogen, C1-13 alkyl, aryl and C7-13 aralkyl
and n is an integer of 1 to 6, whereby CnH2n+1 is C1-6 alkyl or a pharmaceutically acceptable salt of any such compound
with the proviso that the compound is not one of 1-ethyl-2-(1xe2x80x2-hydroxyethyl)-3-hydroxypyridin-4-one and 1-methyl-2-hydroxymethyl-3-hydroxypyridoin-4-one.
Preferably at least one of R, R1 or R7 is such as to form a 3-ester or ether prodrug. Those skilled in the art will recognise the term 3-ester or ether prodrug to mean compounds wherein the 3-hydroxy group has been esterified with a carboxylic or sulpho acid, or formed into an ether with a C1-6 alkyl or C1-10 aralkyl group which is removed in vivo to provide the free hydroxy compound. Typically such carboxylic acid esters or ethers are of C1-7 type, i.e. the 3-substituent is xe2x80x94Oxe2x80x94R8 or xe2x80x94OC(O)xe2x80x94R8 where R8 is C1-6 alkyl or C1-10 aralkyl.
More preferably R5 and R7 are independently selected from C1-6 alkyl, aryl or aralkyl, e.g. benzyl, which may be substitued with C1-6 alkoxy. More preferably R6 is independently selected from hydrogen or C1-6 alkyl. Most preferably R7 is methyl or ethyl.
The positions 5 and 6 are preferably unsubstituted, ie. R3 and R4 are preferably hydrogen, but may be substituted with conventional pyrdin-4-one substituents as disclosed by the prior art as suitable in iron chelators.
Where R1 is an aliphatic carbon group substituted by hydroxy and that hydroxy is esterified the ester acyl group is preferably of formula xe2x80x94COxe2x80x94R9 where R9 is C1-6 alkyl or C1-10 aryl, more preferably being xe2x80x94CO-Phenyl or xe2x80x94CO-hetero, eg. heterocylic rings with one of two nitrogen members and three to five carbons.
R1 and R5 are conveniently independently selected C1-6 alkyl, preferably methyl or ethyl, but preferably may be a hydroxy, alkoxy or esterified hydroxy terminated C1-6 alkyl group. Where R1 is a hydroxy terminated alkyl it is advantageous that the alkyl group is of 3 to 6 carbons long, more preferably being 3 carbons long, e.g. where R1 is xe2x80x94(CH2)3xe2x80x94OH, as such compounds are known to be metabolised in vivo to the corresponding xe2x80x94(CH2)2xe2x80x94CO2H derivative with consequent advantages of low DpH7.4 after metabolism, e.g. in the liver.
Most preferred compounds are of the type where R2 is of groups (i) or (ii).
More preferably R2 is a group xe2x80x94CR6R6OR7 wherein R6 is independently selected at each occurrence from hydrogen, C1-13 alkyl or C6 aryl and R7 is C1-6 alkyl, more preferably methyl or ethyl. An alternate preferred group for R2 is xe2x80x94CONHxe2x80x94R5.
Integer xe2x80x98nxe2x80x99 is preferably 1 such that xe2x80x94CnH2n+1 is preferably methyl or ethyl.
Still more preferred compounds of the invention have a DpH7.4 as determined in an octanol/MOPS pH 7.4 system of in excess of 0.1, more preferably in excess of 1, more preferably being metabolised in vivo to a metabolite having a DpH7.4 of less than 1, more preferably less than 0.1 and still more preferably less than 0.001, as set out in the criteria above. Some compounds of the invention however have potent efficacy without being of high DpH7.4 and without need for metabolism from prodrug forms.
A second aspect of the present invention provides processes for preparation of new compounds of the invention, a third provides novel intermediates for use in these processes, a fourth provides the use of the compounds in therapy, a fifth provides their use in manufacture of medicaments and a sixth provides pharmaceutical compositions comprising them.
The process of the invention is broadly that as set out in any one or more of Schemes 1, 2, 3, 4 and 5. The preferred process comprises all relevant steps of these schemes for a given compound of the invention, Those skilled in the art will readily produce free compounds from the salts shown by conventional techniques.
Novel intermediates of the invention are of formula (IIb), (IIc) and (III) of Scheme 1 (IVa), (IVb) and (IVc) of Scheme 2, (VI), (VII) and (VIII) of Scheme 3 and (X), (XI), (XII) of Scheme 4 and compounds (3) to (5) and 2, 6-substituted lower alkyloxy analogues thereof of Scheme 5.
Thus a first process of the invention comprises the reaction of a 2-(1xe2x80x2-hydroxyalkyl)-3-hydroxy-pyran-4(1H)-one of formula (IIa) 
where R10 is a group as defined in R6 
with benzaldehyde dimethyl acetal to provide the corresponding 8-oxo-4,8-dihydro-2-phenyl-4H[3,2-d]-m-dioxin of formula (IIb), 
reacting that compound with a compound R1NH2 to give the corresponding pyridino dioxin of formula (Ic) 
and reducing that with hydrogen to give the corresponding 2-hydroxyalkyl-pyridin-4(1H)-one.
A second process of the invention comprises the protection of the 3-hydroxyl group of a 2-(1xe2x80x2-hydroxyalkyl)-3-hydroxy-pyran-4(1H)-one of formula (IV), 
eg. using a benzyl halide, preferably benzyl bromide to give a compound (IVa) 
alkylating the 2-(1xe2x80x2-hydroxy) group, eg. with an alkyl halide such as alkyl iodide to, reacting the product thereof (IVb) 
with a compound R1NH2 to provide the corresponding 2-hydroxyalkyl-pyridin-4(1H)-one (IVc) 
and reducing that to provide the correpsonding unprotected compound.
A third process of the present invention reacts a 2-carboxyl-3-benzoyloxy-pyran-4(1H)-one of formula (IXd), that optionally being provied by oxidising the corresponding formyl compound (IXc) eg. with sulfamic acid and sodium chlorite, 
with mercaptothiazoline, eg. in the presence of dicyclocarbodiimide and dimethylaminopyridine to provide the corresponding 2-carbonyl-thiazolidine-2-thione of formula (X), 
reacts that with a compound R5NH2 to give the corresponding 2-amido compound of of formula (XI), 
reacting that with a compound R1NH2 to give the corresponding 2-amido-pyridin-4-one compound of formula (XII) 
and optionally reducing that to provide the corresponding 2-hydroxyalkyl-pyridin-4(1H)-one.
Novel intermediates are the 8-oxo-4,8-dihydro-2-phenyl-4H[3,2-d]-m-dioxins, 2-(1-alkoxyoxyalkyl)-3-hydroxy-pyran-4(1H)-ones and corresponding 2-carbonyl-thiazolidine-2-thiones corresponding to the compounds of Formula I.
A fourth process of the invention reacts kojic acid with formaldehyde to give a 2,6 hydroxymethyl substituted pyran-4-(1H)-one intermediate, protects the 3-hydroxy group, eg. with benzylation, alkylates the two hydroxymethyl groups and then converts the pyran to a pyridone with the required amine. In this manner compounds that are achiral can be accessed.
Also provided within formula (I) are novel compounds which are metabolites of the preferred prodrug compounds of the first aspect of the invention but which have DpH7.4 less than 1; these also being active iron III chelating agents once the compounds of the first aspect have been metabolised eg. in the liver, to remove any ether or ester protecting group where that was required to provide a DpH7.4 of 1 or above. For example in compound CP362 below, the methyl group (R in formula I above), is removed in vivo resulting in a drop in DpH7.4 to give the compound of formula I wherein R is hydrogen, R2 is CH(OH)CH3, R1 is ethyl and R3 and R4 are hydrogen. This compounds 1-methyl-(2-hydroxymethyl)-3-hydroxypyridin-4-one and 1-ethyl-2-(1xe2x80x2hydroxyethyl)-3-hydroxypyrid-4-one are known metabolites of compounds CP94 and CP20 respectively.
Those skilled in the art will readily appreciate that some of these compounds will be known already, but in so far as compounds are novel they are also rendered inventive by their relationship as unobviously active metabolites of the novel compounds of the first aspect. Particularly provided is the provision of such metabolites xe2x80x98for use in therapyxe2x80x99 eg. xe2x80x98for use in therapy of iron related disordersxe2x80x99 and in methods of therapy. These compounds, while not of ideal DpH7.4 for oral activity, will still be of potential use by parenteral or other route of administration.
Salts of the compounds of the invention may readily be formed by reaction of the compound with the appropriate base or acid under suitable conditions. Zwitterionic forms, where appropriate, may conveniently be obtained by freeze drying an aqueous solution at a selected pH. Freeze drying of an aqueous solution whose pH has been adjusted to 7.0 or to greater than 9.0 with the desired base provides a convenient route to a salt of that base. Salts with acids may conveniently be obtained by recrystallization of the compound of formula (I) from an aqueous/organic solution for example the hydrochloride being obtained on recrystallization from a dilute hydrochloric acid/ethanol solution.
Pro-drugs may be formed by reaction of any free hydroxy group compound of formula (I) or a derivative thereof with the appropriate reagent, in particular with an organic acid or derivative thereof, for example as described in U.S. Pat. No. 4,908,371 (incorporated herein by reference) and/or with an alcohol or phenol, for example using standard esterification procedures.
The compounds of formula (I) may be formulated with a physiologically acceptable diluent or carrier for use as pharmaceuticals for veterinary, for example in a mammalian context, and particularly for human use, by a variety of methods. For instance, they may be applied as a composition incorporating a liquid diluent or carrier, for example an aqueous or oily solution, suspension or emulsion, which may often be employed in injectable form for parenteral administration and therefore may conveniently be sterile and pyrogen free. Oral administration is preferred for the preferred compounds of the invention. Although compositions for this purpose may incorporate a liquid diluent or carrier, it is more usual to use a solid, for example a conventional solid carrier material such as starch, lactose, dextrin or magnesium stearate. Such solid compositions may conveniently be of a formed type, for example as tablets, capsules (including spansules), etc.
Other forms of administration than by injection or through the oral route may also be considered in both human and veterinary contexts, for example the use of suppositories or pessaries. Another form of pharamceutical composition is one for buccal or nasal administration, for example lozenges, nose drops or an aerosol spray. Thus, the invention further includes a pharmaceutical composition comprising a 3-hydroxypyridin-2,3-one drug or prodrug of formula (I) as defined hereinbefore together with a physiologically acceptable diluent or carrier.
Compositions may be formulated in unit dosage form, i.e. in the form of discrete portions each comprising a unit dose, or a multiple or sub-multiple of a unit dose. The dosage of active compound given will depend on various factors, including the particular compound employed in the composition and the mode of administration and type of disease be treated, eg. whether for iron overload as in thalessemia or for use in treating iron dependent parasites eg. malaria
Typical dosages for use in human therapy will usually lie in the region of about 0.1 to 50 g daily, preferably 0.5 g to 20 g daily, particularly from about 1 or 2 g to 10 or 15 g daily, for example about 5 g, veterinary doses being on a similar g/kg body weight ratio. However, it will be appreciated that it may be appropriate under certain circumstances to give daily dosages either below or above these levels. Where desired, more than one compound according to the present invention may be administered in the pharmaceutical composition, when the total dosage will usually correspond to those discussed above, or, indeed, other active compounds may be included in the composition.
The present invention will now be described by way of illustration only by reference to the following non-limiting Examples, Tables, Schemes and Figures. Further examples of the invention will occur to those skilled in the art in the light of these.
Tables
Table 1: shows compound codes, structures, DpH7.4 (also known as Kpart), pKa, Logxcex23, pM and in vivo iron mobilisation data for compounds of the invention where R2 is of type (v), both active agents for oral administration and their metabolites, the latter being suitable for parenteral or other non-oral route administration.
Table 2: summarises Table 1 with significant pKa2 and comparative data added.
Table 3: shows compound codes, structures, DpH7.4 (also known as Kpart), pKa, Logxcex23, pM and in vivo iron mobilisation data for compounds of the invention where R2 is of type (i).
Table 4: shows compound codes, structures, DpH7.4 (also known as Kpart), pKa, Logxcex23, pM and in vivo iron mobilisation data for compounds of the invention where R2 and R4 are of type (i).
Schemes
Scheme 1 shows the reaction scheme for synthesis of novel intermediates from compounds of formula (IIa) to compounds of formula (III)
Scheme 2 shows the reaction scheme for synthesis of novel intermediates from compounds (IV) to orally active compounds (V) and
Scheme 3 shows the reaction scheme for formation of R1 ester type oral active compounds.
Scheme 4 shows the reaction scheme for synthesis of novel intermediates from compounds (IX) to amide products (XII) and (XIH).
Scheme 5 shows the preparatory to 2,6 dialkoxymethyl substituted compounds of the invention.